The invention generally relates to brake systems and more particularly relates to a process for shortening the braking distance of a vehicle.
A process for shortening the braking distance is well-known from DE 89 11 963 U1 where on the basis of two present signals a pre-braking action is started for a duration of approx. 0.5 s. At the same time the first signal is triggered by the driver activating a switch. This switch is so arranged that it is either operated by the left foot or one hand and in case of the manual operation the switch is preferably so arranged that the hand does not have to be removed from the steering wheel. The second signal is triggered by recording the speed the driver uses to remove his foot from the accelerator. If this speed is above a certain threshold value pre-braking is automatically started.
In case of this well-known process it is disadvantageous that the driver must carry out a control function that is unusual when driving a vehicle, meaning he/she has to operate a switch with the left foot and one hand, respectively.
Therefore a process is proposed in the genus forming DE 40 28 290 C1 where a larger brake pressure is automatically created than the one resulting from the position of the brake pedal when the speed the brake pedal is operated with exceeds a predetermined value. This is the only criterion for triggering the automatic braking action. In comparison to the process well-known from DE 89 11 963 U1 this process is advantageous since the driver of a vehicle equipped with a so-called brake assistant triggering an automatic brake action does not have to specifically adjust his/her behavior to it, but is able to operate the individual operational controls, in particular the brake pedal, in the usual way.
Nevertheless, a panic situation is recognized and a brake action carried out that correspondingly decelerates faster.
This process has proved its worth in panic situations since the braking distance can be shortened and an accident avoided.
In this process a maximum brake pressure is created by the brake servo unit after the automatic brake action has been triggered in order to shorten the braking distance to the maximum. The automatic brake action is ended when the brake pressure applied to the brake pedal decreases. Since the brake servo unit is automatically activated, the brake pedal pressure is able to reduce itself automatically since the pedal resistance decreases. As a result an unintentional deactivation of the automatic brake action may be caused. Therefore the automatic brake action can be ended without the driver of the vehicle wanting or intending it.
On the other hand the automatic brake action may be triggered unintentionally by a driver reacting quickly to a change in the driving situation causing a maximum of the vehicle""s deceleration without this being necessary or desired. In certain driving situations such a surprising, unintentionally strong braking may result in an disturbance of the traffic flow, particularly in case of dense lines of traffic, or it may even case an accident with a following vehicle.
Although it is simple for the driver of a corresponding vehicle to opoperate this well-known process for shortening the braking distance in his usual way, it may, however, in certain situations result in an unintentionally too low or too high a deceleration of the vehicle. Thus the driver does not always have the complete control of his/her vehicle.
Brake servo units suitable for such processes to shorten the braking distance that can be controlled either mechanically by means of an control bar or electrically by means of a solenoid are well-known from DE 43 24 205 A1 and DE 195 48 705 A1.
The invention is based upon the task to create a process for shortening the braking distance for which the driver of a vehicle does not have to change his behavior, yet is carrying out a suitable deceleration of the vehicle in all driving situations and which enables the driver to maintain safe control of his/her vehicle even during a braking action decelerating more strongly.
According to the process in accordance with the present invention a danger potential is determined showing the probability that the vehicle to be braked will be involved in an accident. In accordance with the danger potential the amplification factor of the brake servo unit is increased in a dangerous situation.
Thus the process in accordance with the invention distinguishes itself from the one well-known out of DE 40 28 290 C1 essentially by the fact that during an automatic brake action there is no need for a maximum deceleration but that the deceleration may take on variable values that are lower for a lower danger potential than for a higher one. This triggers a brake action adjusted to the driving situation that can be considerably better controlled by the driver than a very sudden start of a maximum deceleration.
The inventors of the present invention call a device controlling a process in accordance with the invention a so-called xe2x80x9canalogous brake assistantxe2x80x9d. This should give expression to the fact that the process in accordance with the invention as a rule brakes with continuously adjustable, variable deceleration values whilst the process known from DE 40 28 290 C1 only switches over xe2x80x9cdigitallyxe2x80x9d between a mechanically controlled braking and an automatic full brake application.